Induction of Two-dimensional Growth and Hair Formation by Blue Light in the Brown Alga Scytosiphon lomentaria

Abstract

Summary Plants of Scytosiphon lomentaria grown in blue light form two-dimensional crusts and bear long, multicellular hairs, whereas the prostrate system of plants in red light consists entirely of sparingly-branched and mostly uniseriate filaments, which are completely hairless. The early stages in the morphogenesis of this species have been studied in sporelings growing at similar rates in white, blue, green and red light. After 6 days, plants grown in blue and white light were shorter and broader than plants of identical size in red and green, and almost all plants in blue had formed hairs, whereas red-grown plants were all without hairs. Both of these responses could be induced to occur in red-grown plants by 24–48 h of blue light at an irradiance of 2.3 nE × cm-2 × s-1, and the action spectra for both responses peaked in the region 4207#x2013;450 nm, with additional peaks at shorter and longer blue wavelengths, and in the near-UV. Red and far-red light was completely ineffective. The action spectrum for photosynthesis in young sporelings, however, peaked in red (670–680 nm) and blue (420–450 nm) wavelengths. Substantial photosynthesis also occurred at 540 and 630 nm, although the photosynthesis of red-grown plants was higher at these subsidiary wavelengths than in blue-grown plants. The results indicate that the induction of two-dimensional growth and of hair formation in Scytosiphon are specific morphogenesic effects of blue light, which occur independently of photosynthesis and growth.